Molded plastic dispensing closures, that can be molded at high production rates and with close tolerances, have met with widespread commercial acceptance for dispensing products too numerous to categorize or list. Known dispensing closures usually include (1) a closure body that is secured to the neck of the container holding the product to be dispensed or discharged, (2) a lid that can be pivoted between an open, or discharging position, and a closed position, and (3) a resilient formed hinge joining the lid to the closure body. Such resilient, or "living" hinge may be integrally molded with the lid and closure body, and such "living" hinge enables the lid to be pivoted relative to the closure for the life expectancy of the closure. It should be noted that the "living" hinges are but a few thousandths of an inch in thickness, and are subjected to significant stressing and/or operating forces.
In order to properly stress the "living" hinge as the lid is pivoted between its opened and closed positions, diverse camming mechanisms have been utilized. For example, as shown in U.S. Pat. No. 4,220,248, granted Sep. 2, 1980, to Woodrow S. Wilson and Robert E. Hazard, upstanding resilient posts (50) project upwardly from an upper surface (28) of the closure body and coact with cams, or camming surfaces (52) defined at the lower edge of the skirt (44) of the lid (14). The cams contact, and deform, the resilient posts during movement of the lid, and enhance the successful operation of "living" hinge (16) by temporarily deforming same, within its elastic limits, as the lid is urged between its opened, and closed, position.
A similar camming action is achieved by cooperating, dissimilarly oriented posts or tabs situated on the top surface of the closure body and the underside of the lid, as shown in U.S Pat. No. 4,158,902, granted in June 1979 to Milton Chernack et al.
Another dispensing closure of particular interest is shown in U.S. Pat. No. 4,377,247, granted Mar. 22, 1983 to Robert E. Hazard and Woodrow S. Wilson. The dispensing closure depicted in the Hazard et al patent provides a camming action by virtue of the engagement of the lower edges (52) on the skirt (40) of the lid (14) engaging the upwardly extending, flat wall (22) formed on the upper surface of the closure body, in the vicinity of the "living" hinge (16). The closure body is sealed by a sloping top (18) that includes the flat wall, and a holder (32) is formed to locate the "living" hinge so that the hinge and closure body are joined together.
Further improvements in the camming action defined between the lid and the closure body of a dispensing closure, to temporarily deform the "living" hinge joining the lid to the closure body, are shown in U.S. Pat. No. 4,625,898, granted Dec. 2, 1986, to Robert E. Hazard. Such patent discloses two embodiments of integrally molded, unitary, plastic dispensing closures comprising a body, a lid, and a "living" hinge that joins the lid to the body. In the preferred embodiment of FIGS. 11-18, recesses (436, 438) are formed at the rear of the closure body (402) to accommodate the cams, or lugs (432, 434) when the lid (404) is in its closed position. In the alternative embodiment of FIGS. 19-24, recesses (544; 546) are formed in the skirt of the lid to accept upwardly extending posts (522, 524), and a cavity (518) is defined in the upper surface of the closure body to accept cams, or lugs (534, 536), depending below the lid.
In order to insure that the "living" hinge is properly stressed, and is capable of stretching sufficiently to empower the snap-acting movement of the lid between its opened and closed positions, dispensing closures are usually molded in the opened position. After molding, lids are snapped shut while the plastic remains at an elevated temperature. However, the camming members defined between the lid and the upper surfaces of the body tend to collapse when the lid is closed, and/or the camming members may dig into, or penetrate, the cooperating surfaces used to stress same. Also, in some instances, the "living" hinge may stretch excessively. All of these problems contribute to a higher than desirable rate of closure rejects, which, in turn, adversely impacts upon the manufacturing costs for such dispensing closures. Even a fraction of a penny difference in manufacturing costs, per closure, can have a major impact in the highly competitive, cost-conscious, marketplace.
While molded plastic dispensing closures described above, as well as other dispensing closures, have met with widespread commercial acceptance, because of satisfactory operation, relatively low cost, and aesthetic appeal for mass marketed products such as hair care products and foodstuffs, several operational shortcomings have been encountered, which remain unaddressed. These shortcomings center about the "living" hinge, and the camming mechanisms for deforming, or stretching such hinge, within its elastic limits.
Known molded plastic dispensing closures, as exemplified by the patented structures discussed above, are configured so that all, or at least almost all, of the pivoting movement of the lid between its opened and closed positions is attributable to the temporary, plastic deformation, or stretching, of the "living" hinge. To counteract the harmful effects of the repeated stretching of the "living" hinge, such hinges are made thicker than otherwise necessary. Also, the camming mechanisms defined between the lid and the closure, of necessity, require significant interference between the interacting components to deform the "living" hinge, even momentarily. Such interference between the interacting components requires very close molding tolerances, and causes a high incidence of hinge breakage.
In some instances, the "living" hinge is deformed beyond its elastic limit, and the hinge loses its resiliency, leading to customer complaints. Additionally, at low temperatures, the "living" hinge becomes embrittled, and performs poorly, thus limiting the potential applications for dispensing closures utilizing such component. At the very least, the repeated deformation of the "living" hinge, particularly in the areas where the hinge has been thickened, causes whitening, or discoloration, of the hinge, thereby reducing the aesthetic appeal of the closure.
One known solution for combatting the deficiencies detailed above calls for an elastomer additive to be introduced into the plastic, prior to molding same, so that the "living" hinge will stretch an extra fraction of an inch before exceeding its plastic limit. The elastomer additive, however, is fairly costly and must be blended with care in the molding process; also, the desired glossy finish of the molded polymeric plastic is more easily scuffed and abraded in the presence of the elastomer additive.
Another known solution for combatting the deficiencies noted above revolves about the addition of a lubricant to the polymeric plastic prior to molding same; the lubricant reduces the tendency of the camming members on the skirt of the lid from penetrating, or indenting, the upstanding member(s), such as posts, walls, tabs, or the like, adjacent the "living" hinge. The lubricant facilitates the sliding action of the camming members, despite the high stresses inherent in the design of such dispensing closures. The addition of the lubricant, however, dulls the surface finish of the molded dispensing closure, increases the cost and complexity of manufacturing the closure, and causes problems with the internal threads in the closure body that secure the closure onto the container for the product to be dispensed.
The elastomer additive, and the lubricant, obviously introduce additional complexities and costs in the molding process, lead to defective closures, and complicate the re-grinding and re-cycling of defective closures. Thus, more feasible solutions to the on-going problems associated with dispensing closures utilizing living hinges, are still sought, and promise significant benefits to the manufacturer, and ultimately, to the consumer.